Control method of magnetic disk unit and magnetic disk unit for use in such method

ABSTRACT

In a magnetic disk unit having a load/unload function of a magnetic head for a magnetic disk, the magnetic disk and the magnetic head are prevented from contacting with each other and damage thereto is avoided by utilizing a shallow dual-step subambient pressure slider and carrying out loading/unloading at a rotational speed lower than a rated rotational speed of the normally operated magnetic disk at which writing and reading (R/W) data to and from the magnetic disk by the magnetic head is done.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a control technique of a magnetic disk unit and a magnetic disk unit for use in such a method. Specifically, it relates to a technique which can be effectively applied to a control technique and the like of a magnetic disk unit having a load/unload system.

[0003] 2. Description of the Related Art

[0004] In recent years, magnetic disk units are having higher recording density, magnetic disks are having less surface roughness, and flying heights of magnetic heads are getting lower. Therefore, in a conventional magnetic disk unit of contact-start-stop type wherein a magnetic head stays on a magnetic disk when a rotation of the magnetic disk is stopped, adsorption is apt to occur between the magnetic disk and the magnetic head, which sometimes makes it difficult to start up the magnetic disk.

[0005] As one of the solutions for this technical problem, a system called a load/unload system in which the magnetic head is loaded on and unloaded from the magnetic disk is sometimes utilized. When the magnetic disk is stopped, this system keeps the magnetic head away from the magnetic disk (unloaded state). Further, when the disk is rotating to write and read data, the system places (loads) the magnetic head above the magnetic disk to be in a flying state.

[0006] Now, a load/unload operation of the load/unload system will be described.

[0007] First, a load operation of the load/unload will be described. When the unit is stopped, the magnetic head stays away from the magnetic disk as a lift tab attached to the magnetic head moves along a ramp (sloping path). When the unit is turned on, the rotation of the magnetic disk is started by a spindle motor. Upon a rated rotational speed being achieved, the magnetic head in a retreated state descends the ramp through the lift tab and takes a position (loaded) above the magnetic disk in a flying manner.

[0008] Next, an unload operation will be described. During the disk rotation, when an instruction to stop the unit is issued, the magnetic head above the magnetic disk makes the lift tab slide along the ramp through a moving action of an actuator to ascend the ramp and retreats from the magnetic disk, and the motor is stopped.

[0009] Now, a description of a subambient pressure slider in the magnetic disk will be made. The subambient pressure slider has a positive-pressure generating portion and a negative-pressure generating portion on a flying surface opposing the magnetic disk. Further, it is flying above the disk according to a proper balance between itself and the load.

[0010] When unloading, the lift tab runs onto the ramp and the magnetic head tends to stay away from the magnetic disk. At this time, since a negative-pressure portion exists in part of the flying surface of the slider, a reactive force in the direction of attracting the slider to a surface of the magnetic disk is produced to break the flying posture. Further, in the course of unloading in which the magnetic head runs onto the ramp, the magnetic head collides with the magnetic disk, thereby increasing the possibility of causing abrasion and damage to the magnetic disk and the magnetic head, which has been a problem to be solved technically.

[0011] Further, to reduce the data-access time, when using a 3.5-inch magnetic disk unit at a rotational speed higher than 10,000 rpm instead of a conventional 2.5-inch magnetic disk unit at 4,200 rpm, the impact of the collision between the magnetic head and the magnetic disk is intensified, thereby increasing the possibility of causing abrasion and damage to the magnetic disk and the magnetic head.

[0012] The solution to avoid the damage when loading and unloading may be to decrease the moving speed of the magnetic head. However, it brings about another technical problem such as prolongation of time for loading and unloading.

SUMMARY OF THE INVENTION

[0013] It is an object of the present invention to provide a magnetic disk unit in which damage to a magnetic head and a magnetic disk, etc. caused by the contact or collision during load/unload operation is reduced as well as a control technique therefor.

[0014] In a control method of a magnetic disk unit, which comprises a magnetic disk, a head writing and reading data to and from the magnetic disk, an actuator positioning the head on the magnetic disk, and a load/unload system unloading by taking the head away from the magnetic disk and loading by bringing the head on the magnetic disk, at least either loading or unloading is carried out at a second rotational speed being lower than a first rotational speed at which writing and reading to and from the magnetic disk by the head is carried out.

[0015] Also, according to the present invention, in a control method of a magnetic disk unit, which comprises a magnetic disk, a head writing and reading data to and from the magnetic disk, an actuator positioning the head on the magnetic disk, a load/unload system unloading by taking the head away from the magnetic disk and loading by bringing the head on the magnetic disk, a control logic which executes at least either loading or unloading by a second rotational speed being lower than a first rotational speed at which writing and reading to and from the magnetic disk by the head is done is provided.

[0016] More specifically, as an example, the rotation speed of the magnetic disk when loading/unloading is set to be a half to one-tenth of the rotational speed of a usual R/W operation.

[0017] Further, as a head slider making up part of the magnetic head, a shallow dual-step subambient pressure slider whose flying height gets higher as a result of the lower disk rotational speed during loading/unloading is used.

[0018] Also, the upper limit of the moving speed of the magnetic head during loading/unloading is set to be 0.1 m/s.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0020]FIG. 1 is a chart showing a control method of a magnetic disk unit according to one embodiment of the invention and an example of the operation of the magnetic disk;

[0021]FIG. 2 is a chart showing a control method of a magnetic disk unit according to one embodiment of the invention and another example of the operation of the magnetic disk;

[0022]FIG. 3 is a chart showing a control method of a magnetic disk unit according to one embodiment of the invention and another example of the operation of the magnetic disk;

[0023]FIG. 4 is a flowchart showing a control method of a magnetic disk unit according to one embodiment of the invention and an example of the operation of the magnetic disk;

[0024]FIG. 5 is a schematic plan view showing an example of an internal structure of a magnetic disk unit in which a control method of the magnetic disk unit according to one embodiment of the invention is implemented;

[0025]FIG. 6 is a schematic cross section view showing an example of an internal structure of a magnetic disk unit in which a control method of the magnetic disk unit according to one embodiment of the invention is implemented;

[0026]FIG. 7A is a chart showing an interrelationship of a flying height of a slider making up part of a magnetic head and a disk (magnetic disk) rotational speed, and FIG. 7B is an explanatory drawing comparing effects of a shallow dual-step subambient pressure slider according to an embodiment of the invention and a related art;

[0027]FIG. 8 is a chart illustrating an interrelationship of a magnetic-disk rotational speed and an incidence of damage caused by the contact between the head and the magnetic disk;

[0028]FIG. 9 is an explanatory drawing showing an example of working effects of a magnetic disk unit in which a control method of the magnetic disk unit according to one embodiment of the present invention is implemented;

[0029]FIGS. 10A, 10B, and 10C are a plan view and perspective views, respectively, showing an example of a structure of a shallow dual-step subambient pressure slider used in a magnetic disk unit in which a control method of the magnetic disk unit according to one embodiment of the invention is implemented;

[0030]FIG. 11 is an explanatory drawing showing an example of an operation of a shallow dual-step subambient pressure slider used in a magnetic disk unit in which a control method of the magnetic disk unit according to one embodiment of the invention is implemented; and

[0031]FIG. 12A is a plan view, and FIGS. 12B and 12C are perspective views, respectively, showing a subambient pressure slider of a related art of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] With reference to the drawings, an embodiment of the present invention will be described in detail.

[0033] FIGS. 1 to 3 are charts showing control methods of the magnetic disk unit according to one embodiment of the present invention and an example of the operation of the magnetic disk unit. FIG. 4 is a flowchart showing a control method of a magnetic disk unit according to one embodiment of the invention and an example of the operation of the magnetic disk unit.

[0034] Also, FIG. 5 is a schematic plan view showing an example of an internal structure of the magnetic disk unit in which the control method of the magnetic disk unit according to one embodiment of the present invention is implemented; and FIG. 6 is its schematic cross section.

[0035] The magnetic disk unit according to the present embodiment shown in FIGS. 5 and 6 comprises a magnetic disk 1 recording data, a spindle 2 a supporting the magnetic disk 1, a motor 2 rotating the magnetic disk 1 through the spindle 2 a, a magnetic head 3 writing and reading data to and from the magnetic disk 1, an actuator system 4 such as a voice coil motor controlling the positioning of the magnetic head 3 with respect to the magnetic disk 1 through a suspension 5 rotating about a pivot shaft 4 a in a plane parallel to the magnetic disk 1, and a load/unload system mechanically separating the magnetic head 3 from the magnetic disk 1 when unloading, and comprising a lift tab 7 fixed on the side of the magnetic head 3 and a ramp 6 provided on the outer side of the magnetic disk 1 within the rotating range of the lift tab 7 by the actuator system 4 and having a sloping contact surface 6 a on which the lift tab 7 slides.

[0036] Further, the magnetic disk unit of the present embodiment has a unit control section 8 controlling rotation of the magnetic disk 1 by the motor 2, detection of the rotating condition, positioning of the magnetic head 3 and a load/unload operation by the actuator system 4, operation by the magnetic head 3, and giving and receiving of data to and from host devices, not shown, etc.

[0037] The magnetic disk 1 is rotated by the motor 2, the actuator system 4 is activated by the load/unload operation to load the magnetic head 3 on the magnetic disk 1, and the loading status is achieved by a load spring 5 urging in the direction to press the magnetic head 3 against the magnetic disk 1. During the unload operation, the actuator system 4 functions so as to move the magnetic head 3 and the lift tab 7 toward the outside of the magnetic disk 1 to unload the magnetic head 3, and the lift tab 7 runs onto the ramp 6 to lose an urging force of the load spring 5, achieving the unloaded status.

[0038] According to the present embodiment, the magnetic head 3 comprises a shallow dual-step subambient pressure slider 3-1 having a structure shown in FIG. 10, and a combined head 3-2 being supported by a portion of the shallow dual-step subambient pressure slider 3-1 and comprising, for example, a thin-film coil recording head and a reproducing head including a magnetoresistance-effect element.

[0039] In FIG. 7A, a chart to show an interrelation of flying height of a slider making up part of the magnetic head and a disk (magnetic disk) rotational speed is shown. The vertical axis shows a flying height of the slider and the horizontal axis shows a disk rotational speed.

[0040] Now, a description of the slider will be made. FIG. 12 shows a subambient pressure slider 300 according to a related art of the present invention. In this subambient pressure slider 300, a plurality of rail-like pads 300 b is provided in an extended condition on a flying surface 300 a opposing the magnetic disk, and a tapered portion 300 c is formed on the inflow-end side of airflow produced by the rotation of the magnetic disk. Also, a combined head 301 is positioned at the end face on the other side of the tapered portion 300 c. Such structured subambient pressure slider 300 has a characteristic that the flying height Hf of the head rises as the rotational speed of the magnetic disk 1 gets higher.

[0041] On the other hand, a shallow-dual step subambient pressure slider 3-1 of the present embodiment shown in FIG. 10 has such a structure that rail portions 3-1 b, 3-1 c, and pad portions 3-1 d, 3-1 e on each of the rail portions 3-1 b, 3-1 c are formed in a multi-stepped manner on the flying surface 3-1 a opposing the magnetic disk 1. Also, the above-described combined head 3-2 is positioned on the rail portion 3-1 c on the outflow-end side of airflow produced by the rotation of the magnetic disk 1 and on an end face of the pad portion 3-1 e.

[0042]FIG. 11 is a schematic cross section of a shallow dual-step subambient pressure slider 3-1. According to the slider 3-1, flying characteristics such as flying height are controlled by adjusting heights of an upper surface (shallow groove surface) of the rail portions 3-1 b, 3-1 c and an upper surface (pad surface) of the pad portions 3-1 d, 3-1 e with respect to a bottom (bleed surface) of the deepest groove in a periphery of the rail portions 3-1 b, 3-1 c. For example, as shown in FIG. 11, the flying height Hf of the shallow dual-step subambient pressure slider 3-1 becomes higher (lower) as the distance between the bleed surface and the shallow groove surface gets shorter (longer).

[0043] In the case of the shallow dual-step subambient pressure slider 3-1 of the present embodiment in which the tapered portion 300 c of the subambient pressure slider 300 of the related art in FIG. 12 is removed, as described, the following flying height characteristic is obtained by changing shapes of the rail portions 3-1 b, 3-1 c of the slider. Namely, the flying height of the magnetic head 3 is lowered (reaches a first flying height Hf1) as the rotational speed of the magnetic disk 1 gets higher. On the contrary, when the rotational speed of the magnetic disk 1 is lowered, the flying height of the magnetic head 3 is raised (reaches a second flying height Hf2). By making use of such a flying characteristic of the shallow dual-step subambient pressure slider 3-1, as shown in FIG. 7B, in comparison with the subambient pressure slider 300 of the related art, an effect of reducing the contact shock between the magnetic disk 1 and the magnetic head 3 during loading/unloading is obtained, thereby avoiding damage thereto.

[0044] Further, as shown in FIG. 7A, one of the characteristics of the shallow dual-step subambient pressure slider 3-1 making up part of the magnetic head 3 of the present embodiment is that the flying height does not vary much and stays at Hf1 after a given rotational speed is achieved.

[0045] Now, a description of lubricant film thickness of the disk will be made. By its nature, lubricant of a disk serves to avoid damage caused by contact and abrasion between the magnetic disk 1 and the magnetic head 3 while the magnetic disk 1 is rotating. When loading/unloading, however, it must not be too thick so as to avoid the contact caused by loading/unloading as much as possible. However, with too little lubricant, it becomes impossible to avoid damage caused by contact and abrasion between the magnetic disk 1 and the magnetic head 3 while the magnetic disk 1 is rotating. In view of the above, the most appropriate lubricant film thickness for loading/unloading is at most 25 Å and at least 8 Å.

[0046] Now, a description of surface roughness of the disk will be made. When loading and/or unloading, what serves most effectively to avoid abrasion and damage of the magnetic disk 1 and the magnetic head 3 is a distance between them during load/unload operation. Therefore, the difference between surface roughness of disks can also reduce damage if they are kept as small as possible. Accordingly, surface roughness of Ra 0.4 nm and Rp 0.8 nm, for example, are preferable for effectively utilizing the magnetic disk 1.

[0047] Now, a description of a moving speed of the magnetic head 3 will be made. During loading/unloading, particularly at a time of unloading, when the shallow dual-step subambient pressure slider 3-1 such as the present embodiment is adopted, suction force is produced between the rotating magnetic disk 1 and the magnetic head 3 on the magnetic disk 1 by a negative-pressure characteristic of the shallow dual-step subambient pressure slider 3-1. In an attempt to separate the magnetic head 3 in this state from the magnetic disk 1, a lift tab 7 on a tip end of a load spring 5 runs onto a sloping contact surface 6 a of a ramp 6 and separate the magnetic head 3 from the magnetic disk 1. At this separating moment, the magnetic disk 1 and the magnetic head 3 come into contact with each other. In particular, the higher the moving speed of the magnetic head 3 gets, the stronger the contacting force grows. Thus, abrasion and damage are easily brought about. On the contrary, the lower the moving speed is, the weaker the contacting force becomes. Thus, the abrasion and damage are not easily brought about. Also, when loading, the higher the moving speed of the magnetic head 3 is, the more likely it is for the magnetic head 3 to contact the magnetic disk 1 the moment it is loaded on the magnetic disk 1. On the contrary, the lower the moving speed of the magnetic head 3 is, the less likely it is for the magnetic head 3 to contact the magnetic disk 1. In view of the above, it is the most preferable for the moving speed of the magnetic head 3 to be 0.1 m/s at the highest.

[0048] Next, rotational speeds of the magnetic disk 1 and damage caused by the contact between the magnetic disk 1 and the magnetic head 3 when loading/unloading will be discussed.

[0049]FIG. 8 shows a chart in which disk rotational speed is entered the horizontal axis and damage caused by the contact between the head and the disk is entered the vertical axis.

[0050] Now, a description of the contact between the magnetic disk 1 and the magnetic head 3 when loading/unloading will be made. When loading/unloading, the magnetic disk 1 and the magnetic head 3 come into contact with each other. Further, damage to the magnetic disk 1 and the magnetic head 3 gets greater as the rotational speed of the magnetic disk 1 gets higher.

[0051] Therefore, according to the present invention, as shown in FIG. 1, at least either loading or unloading is carried out within the range between the rotational speed N1 (N0/2, for example), which is lower than the rated rotational speed N0 at which R/W of data to and from the magnetic disk 1 by the magnetic head 3 is done, and N2 (N0/10, for example). For illustrative reasons, in FIG. 1, the case wherein both the loading and unloading are carried out at rotational speeds N1-N2, which are lower than the rated rotational speed N0, is shown. However, either unloading or loading alone can be carried out at the rotational speeds N1-N2, which are lower than the rated rotational speed N0.

[0052] Further, as illustrated in FIG. 2, rotational rate of acceleration or rotational rate of deceleration in the course of acceleration or deceleration of the magnetic disk 1 when being loaded or unloaded may be selectively lowered. Or, as illustrated in FIG. 3, the rotational speed of the magnetic disk 1 may be set at a predetermined constant rotational speed N3 (=N1−N2) before reaching the rated rotational speed N0, and loading/unloading may be carried out in that state.

[0053] In accordance with the increase of the rotational speed of the magnetic disk 1, as shown in a characteristic chart of the FIG. 7A, the flying height Hf of the subambient pressure slider 300 of the related art gradually increases. Therefore, for example, when rotating the magnetic disk 1 at a high speed of 10,000 rpm or more, it becomes difficult to achieve the objective low flying height and it cannot be helped but to use the shallow dual-step subambient pressure slider 3-1. In the present embodiment, however, loading/unloading are carried out at rotational speeds N1-N2, which are lower than the rated rotational speed N0 at the rated flying height Hf1. Namely, since the loading/unloading are carried out at a higher flying height Hf2, which more effectively prevents the magnetic disk 1 and the magnetic head 3 from colliding with each other.

[0054] Thus, in a high-speed magnetic disk unit in which the shallow dual-step subambient pressure slider 3-1 has to be used, the magnetic disk 1 and the magnetic head 3 are more effectively prevented from being damaged.

[0055] The control of the timing of loading/unloading according to a rotational speed of the magnetic disk 1, as illustrated in FIGS. 1 to 3, can be carried out by control software or firmware installed in the unit control section 8 controlling loading/unloading. FIG. 4 shows a flowchart of an example of the control operation by the control software and firmware, which control the timing of loading/unloading in accordance with the rotational speed of the magnetic disk 1.

[0056]FIG. 9 shows an example of measured results of checking the occurrence of contact between the magnetic disk 1 (disk) and the magnetic head 3 when loading/unloading at various rotational speeds of the magnetic disk 1. As the rotational speed of the magnetic disk 1 gets higher, damage to the magnetic disk 1 and the magnetic head 3 gets greater. On the other hand, the magnetic disk 1 and the magnetic head 3 get greater damage as well when the rotational speed is too low to load and/or unload.

[0057] In view of the above, to reduce an impact of the collision of the magnetic disk 1 and the magnetic head 3 and prevent the damage to them, it is preferable to load and/or unload at rotational speeds N1-N2, which are a half to one-tenth of the conventional rated rotational speed N0 of the magnetic disk.

[0058] As described above, in the magnetic disk unit and its control method according to the present embodiment, contact between the magnetic disk 1 and the magnetic head 3 during loading/unloading is prevented and, further, damage to the magnetic disk 1 and the magnetic head 3 is avoided.

[0059] In other words, it makes it possible to raise the moving speed of the magnetic head 3 at loading/unloading and to shorten the required time for loading/unloading without being concerned with the occurrence of damage to the magnetic disk 1 and the magnetic head 3.

[0060] Further, the reliability of the magnetic disk unit can be improved as well.

[0061] The invention made by the inventor has been specifically described in accordance with the embodiment. The present invention, however, is not limited to the above embodiment, and it is needless to say that it can be altered variously without departing from the spirit of the invention.

[0062] According to the control method of the magnetic disk unit of the present invention, an effect to reduce damage to the magnetic head and the magnetic disk, etc. by the contact and collision during loading/unloading can be obtained.

[0063] According to the magnetic disk unit of the present invention, an effect to reduce damage to the magnetic head and the magnetic disk, etc. by the contact and collision during loading/unloading can be obtained.

[0064] The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to appraise the public of the scope of the present invention, the following claims are made. 

What is claimed is:
 1. A control method of a magnetic disk unit, the magnetic disk unit comprising: a magnetic disk, a head writing and reading data to and from the magnetic disk, an actuator positioning the head on the magnetic disk, and a load/unload system unloading by taking the head away from the magnetic disk and loading by bringing the head on the magnetic disk; wherein the head comprises a slider having a flying characteristic in which a second flying height above the magnetic disk at the second rotational speed is higher than a first flying height above the magnetic disk at the first rotational speed, and wherein at least either loading or unloading is carried out at the second rotational speed being lower than the first rotational speed at which writing and reading data to and from the magnetic disk by the head is carried out.
 2. A control method of the magnetic disk unit according to claim 1 , wherein the second rotational speed is a half to one-tenth of the first rotational speed.
 3. A magnetic disk unit comprising: a magnetic disk, a head writing and reading data to and from the magnetic disk, an actuator positioning the head on the magnetic disk, and a load/unload system unloading by taking the head away from the magnetic disk and loading by bringing the head on the magnetic disk; wherein the head comprises a slider having a flying characteristic in which a second flying height above the magnetic disk at the second rotational speed is higher than a first flying height above the magnetic disk at the first rotational speed, and wherein a control logic is provided so as to execute at least either loading or unloading at the second rotational speed being lower than the first rotational speed at which writing and reading data to and from the magnetic disk by the head is carried out.
 4. A magnetic disk unit according to claim 3 , wherein the second rotational speed is a half to one-tenth of the first rotational speed. 